Motor cortex Flashcards
Describe the difference between decerebrate and decorticate rigidity?
Decerebrate: extension of upper and lower limbs
Decorticate: extension of lower limbs, but flexion of upper limbs
What do cecerebrate and decorticate rigidity result from?
Loss of brain control over spinal cord
In which pathway is the red nucleus found?
What is its function?
Where does it project to?
Lateral corticospinal tract
Initiates flexion in distal musculature
Projects to rubrospinal tract
Contrast the location of the reticular formation and the red nucleus?
Reticular formation: pons and medulla
Red nucleus: midbrain
Describe the inputs to the reticular formation and the red nucleus?
What is the consequence of this?
A lot of drive from cortical inputs, most of which is inhibitory
So, there is tonic inhibitory control over these nuclei, ongoing suppression
What happens when inhibitory control over the reticular formation and red nuclei are lost?
Explain.
Depends on location of lesion
Removal of cortical input to all levels of brainstem > decoritcate rigidity (free running reticular formation > extensors dominant, free running red nucelus > flexion wins out over extensors in arms)
Level of disruption below midbrain > decerebrate rigidity (still disinhibition of reticular formation > extensors dominate)
What does progression from decorticate to decerebrate rigidity signify?
There is a lesion that is progressing to include more and more of the brainstem
Describe Babinski’s sign?
Upgoing plantar reflex (dorsiflexion) and fanning toes
What is Babinski’s sign indicative of?
Loss of brain control over spinal cord
Descending tract damage
When is Babinski’s sign normal?
Why?
In first 12-24 months of life
Brain hasn’t yet developed functional control over spinal cord
DF seems like a sensible response when crawling
Why are monosynpatic reflexes so informative?
Final commmon pathway
Tell us about how the motor neurons are working in the context of everything above them
Part of an hierarchy
What is the general approach to identifying UMN lesions in cranial nerves?
Pattern of loss (rather than UMN/LMN signs seen with spinal motor input)
What is the upper motor neuron input to the cranial nerves called?
Corticobulbar innervation
Describe the pattern of corticobulbar innervation to the cranial nerves?
Bilateral innervation, except to lower face and tongue (contralateral innervation only)
Face: one nucleus for upper, one nucleus for lower
How can upper and lower motor neuron lesions to the facial nerve be identified?
Explain.
Lower motor neuron lesion: both upper and lower facial nuclei affected > weakness of superior and inferior facial muscles
Upper motor neuron lesion: bilateral innervation to upper face > upper face unaffected
However, lower face only receives contraletral innervation > weakness of inferior contralateral facial muscles
What is the beneift of EMG?
High temporal resolution
Very helpful in telling us when a muscle is active or inactive
What are the two components to most motor control?
Anticipation: knowledge of task and preparing for action
Reflex control: negative feedback control of muscle position
Describe the integration between anticipation and reflex control that occurs during the task of catching a ball?
Describe the anticipatory involuntary movements involved in lifting one leg laterally?
Describe the anatomy behind the control of the anticipatory involuntary movements?
Direct cortical pathway that is ipsilateral and joins up with ventral pathways
How do we know that locomotion is controlled by the lumbosacral spinal cord?
Newborn babies and anencephalics exhibit locomotor reflex
At this stage, brain does not have control over spinal cord
Describe the phases of locomotion?
Stance phase: associated with weight bearing, so extensors active, move into flexion at the end
Swing phase: associated with movement, so flexors active, with a bit of extension for grounding at the end
How do decerebrate cats increase speed of locomotion when treadmill speed is increased?
Sesnory information is coming from the limbs
Information from muscle spindle and Golgi tendon organs
Input from periphery to tell you which stage of the locomotion cycle you are in, and what you need to do next
What controls the initiation of the swing phase in locomtion?
Sensory feedback from extensor muscles
Why is cortical input required for locomotion, if the pattern generator is located in the spinal cord?
Motor cortex responsible for sending information down to pattern generator to chnage pattern when we have to do something out of the ordinary
List some of the abnormal gait patterns associated with CNS disorders?
Ataxic gait
Choreaform gait
Hemiparetic gait
Circumducting gait
Parkinsonian gait
